DHCP service on Cisco routers

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May 13th, 2010
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hi experts,


i've enabled DHCP service on a Cisco router with the following requirements:


10.0.0.0 /8 network with usable or lease IPs: 10.0.1.48 - 10.0.1.247


the config i did was below:


ip dhcp-excluded address 10.0.1.1 10.0.1.47

ip dhcp-excluded address 10.0.1.248 10.0.1.255


ip dhcp pool LAN

network 10.0.0.0 255.0.0.0

default-router 10.0.1.1

dns-server 192.169.x.x



i would appreciate if someone would advise if the config would meet the initial requirements or if i need to add more statements for the excluded addresses. i'm thinking that this config might lease an IP of 10.0.0.1 or on the other range not specified on the excluded addresses.

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Jon Marshall Thu, 05/13/2010 - 12:45
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johnlloyd_13 wrote:


hi experts,


i've enabled DHCP service on a Cisco router with the following requirements:


10.0.0.0 /8 network with usable or lease IPs: 10.0.1.48 - 10.0.1.247


the config i did was below:


ip dhcp-excluded address 10.0.1.1 10.0.1.47

ip dhcp-excluded address 10.0.1.248 10.0.1.255


ip dhcp pool LAN

network 10.0.0.0 255.0.0.0

default-router 10.0.1.1

dns-server 192.169.x.x



i would appreciate if someone would advise if the config would meet the initial requirements or if i need to add more statements for the excluded addresses. i'm thinking that this config might lease an IP of 10.0.0.1 or on the other range not specified on the excluded addresses.


John


Yes it could lease out many other addresses.


Could you not just use


ip dhcp pool LAN

network 10.0.1.0 255.255.255.0

etc...


Jon

johnlloyd_13 Thu, 05/13/2010 - 19:31
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thank jon! that was my inital thoughts as well. i would need the SM to be a /8. any other work around? like adding statements on the excluded address just to "unlease" the other address range?

abersven Sun, 06/13/2010 - 10:55
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For 10.0.0.0 /8 network with usable or lease IPs: 10.0.1.48 - 10.0.1.247 you can use the following configuration:


!

ip dhcp-excluded address 10.0.0.0 10.0.1.47

ip dhcp-excluded  address 10.0.1.248 10.255.255.255

!

ip dhcp pool LAN

network 10.0.0.0  255.0.0.0

default-router 10.0.1.1

dns-server 192.169.x.x

!


The network statement is also used to map this dhcp pool to an interface. So I assume that you have an interface within this range. It’s a strange requirement you have when I do not have your whole configuration or the details because I believe that the broadcast address might be wrong on the client compared to what you have on your routers interface. Broadcast address will be 10.255.255.255.



/André

Giuseppe Larosa Mon, 06/14/2010 - 06:07
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Hello John,


in real world using a /8 would be insane, you should define multiple DHCP pools matching the real subnets on the different interfaces


Hope to help

Giuseppe

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